Based on the crystal structure and morphology of ferrite, the preparation processes can be generally divided into: polycrystalline ferrite production process; ferrite chemical process; single - crystal ferrite production process and other special processes, such as polycrystalline ferrite thin films and amorphous ferrite.
Polycrystalline Ferrite Production Process
It is similar to the sintering process commonly used in the ceramic industry and includes the following steps: Metal oxides, carbonates, or other compounds that form ferrite through solid - state reactions are mixed evenly, then ball - milled, dried, and pressed into specific shapes. After pre - sintering at a temperature of about 1000°C, they are ground and mixed thoroughly again. An appropriate amount of binder is added, and they are pressed into the required shape or extruded as a plastic substance into a tubular, rod - like, or strip - like shape. Then they are sintered at a temperature of 1200 - 1400°C. The exact temperature depends on the desired characteristics of the ferrite. During the final sintering process, the environmental conditions in the furnace play an important role.
Ferrite Chemical Process
It is also known as the wet - process or sometimes the chemical co - precipitation method. It is a process method specifically for preparing high - performance ferrite and can be further divided into the neutralization method and the oxidation method. The process is as follows: First, the metal elements required for preparing ferrite are prepared into an ion solution of a certain concentration. Then, an appropriate amount of solution is taken according to the formula for mixing. Ferrite powder is generated through chemical reactions such as neutralization or oxidation. The subsequent process is the same as that introduced before.
Single - Crystal Ferrite Production Process
It is generally the same as the growth of non - metallic single crystals. The growth of Mn - Zn and Ni - Zn - based ferrite single crystals usually uses the Bridgman method. That is, after putting polycrystalline ferrite into a platinum crucible and melting it, the crucible is lowered in an electric furnace with an appropriate temperature gradient, and single crystals are slowly solidified from the bottom of the crucible. In order to make the oxygen partial pressure formed in the molten state uniform, an oxygen partial pressure of several to 100 MPa is required in the furnace during crystal growth.
Preparation of Polycrystalline Ferrite Thin Films
For example, for barium ferrite thin films with vertical magnetization, a new - type opposite - target sputtering device is used for sputtering. For the preparation of garnet single - crystal thin films, the vapor - phase or liquid - phase epitaxial method on single - crystal substrates is mostly used. The detailed process is very similar to the epitaxial method of semiconductor single - crystal thin films.
Preparation of Amorphous Ferrite
At present, the ultra - rapid cooling method and the sputtering method are used. The so - called ultra - rapid cooling method is a method in which the ferrite raw materials and an appropriate amount of metalloid elements are mixed and then, in a high - temperature molten state, suddenly subjected to an ultra - rapid cooling with a large temperature gradient. Research in this area has just begun, and the performance of the finished products is not yet ideal.
